One of the critical endeavors in human medical research is the discovery of genetic abnormalities that produce adverse health consequences. In many cases, specific genes and/or critical diagnostic markers have been identified for use in prenatal and cancer diagnosis, for example.
Conventional procedures for genetic screening and biological dosimetry have utilized invasive procedures, e.g. amniocentesis, to obtain cells for the analysis of karyotypes. The advent of technologies that allow for sequencing entire genomes in relatively short time, and the discovery of circulating cell-free DNA (cfDNA) have provided the opportunity to compare genetic material originating from one chromosome to be compared to that of another without the risks associated with invasive sampling methods. However, the limitations of the existing methods, which include insufficient sensitivity stemming from the limited levels of cfDNA and the special care required in extracting cfDNA, underlie the continuing need for improved methods that would provide inexpensive and reliable diagnosis protocols utilizing cfDNA in a variety of clinical settings.
Conventionally, when blood is collected in the commonly used blood collection tubes, such as EDTA tubes and ACD tubes, the plasma has to be separated from other blood fractions before purifying cfDNA. Plasma is generally separated from other blood components by centrifugation. The reason for the mandatory plasma isolation step is to avoid contaminating the cfDNA with cellular DNA from the white blood cells. In addition to separating the plasma, cfDNA must be purified by, e.g., releasing it from nucleosomes prior to sequencing. Unfortunately, the purification steps associated with conventional techniques for isolating cfDNA increase the cost and complexity of the cfDNA diagnostic procedures.